Another day another thought!
So I found the full version of The Musgrave Ritual totally on accident sung by Indica Watson who plays young Eurus which I will leave here: https://youtu.be/Pd-bGB2jxaQ?feature=shared
And in listening to it, and thinking upon the events of the final problem, I thought of a headcanon.
Do you remember in the flashback we get, I think in season 3, where Sherlock says to John, after he noticed him about to make a new blog entry “Don’t mention the unsolved ones?”
What if Sherlock feels shame about his unsolved cases? After all, although he couldn’t remember it. Technically The Musgrave Ritual technically was his first case, and his first unsolved one. (Since technically he did figure out that Carl Power’s death wasn’t an accident, of course given the lack of police interest in little nine year old Sherlock, Technically Sherlock couldn’t properly solve the case, leaving it part way solved.)
What if, due to not being able to figure out the song meaning when he was young, thus his best friend died, Sherlock feels shame due to the unsolved cases of course he doesn’t know where it comes from because he doesn’t remember the truth of Red Beard.
Maybe it’s why Sherlock has such a strong compulsion to ‘solve’ things. Why he chose to be a detective in the first place. After all Mycroft did say “Every choice you’ve ever made, every path you’ve ever taken, the man you are today is your memory of Eurus.“
Speaking of, although slightly of track, the “every path you’ve ever taken” line, Do you think Mycroft blames Eurus for Sherlock most likely becoming an addict? After all, even if he couldn’t remember, it’s not like that trauma is just gone, it’s why Mycroft monitored Sherlock with bringing up ‘Red Beard’ to monitor his condition.